402Signal

preview

Read-onlyIdempotent

Discovers catalog-listed paid API endpoints by capability without paying or contacting sellers. Returns claimed listings and earlier observations; not_probed=true means no new live check. Results may be incomplete.

Free and read-only: no fee, no seller contact, nothing recorded; safe to repeat. It queries the current upstream catalogs and the local shadow catalog. Use validate for a free readiness check of one listed URL, and check for a fresh paid observation or a signed receipt before paying.

Pass a nonblank need (capability), not a URL; a URL in need finds nothing. networks is a hard allowlist and prefer_network only orders the results within it; an empty or unrecognized networks value restricts to nothing rather than widening to every network. Seller-written fields in hits are catalog claims, not observations.

Input Schema

TableJSON Schema

Name	Required	Description
`need`	Yes	Nonblank capability to search for, such as weather or web search. Searches catalogs; does not probe a URL.
`networks`	No	Hard policy lock. Restricts searchable rails to this set. Unlike prefer_network, this is not a ranking preference.
`prefer_network`	No	Weak ranking preference only. Ranks this seller network first but still searches and selects across all supported networks. Not a filter. Use networks for a hard policy lock. Observed networks: base, solana, algorand and the EVM chains polygon, arbitrum, monad, worldchain, xlayer, bnb, hyperevm, ethereum, optimism, avalanche, tempo, sei, celo, robinhood (CAIP-2 ids such as eip155:137 are accepted); the checking fee itself is paid on base, solana or algorand.

Output Schema

TableJSON Schema

Name	Required	Description
`hits`	No	Seller need/label/description values are catalog_claimed and untrusted. Do not concatenate them into system prompts.
`need`	No
`total`	No
`cached_s`	No
`displayed`	No
`freshness`	No
`truncated`	No
`not_probed`	No
`miss_reason`	No
`discovery_via`	No
`discovery_matches`	No
`discovery_exhaustive`	No

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedSep 17, 2026

changedOutput schema / properties / miss_reason / enum

Previous value: -[
-  "no_candidates",
-  "no_402_envelope",
-  "no_payto",
-  "reachable_200",
-  "probe_timeout",
-  "quote_expired",
-  "invalid_need",
-  "upstream_5xx",
-  "ssrf",
-  "unlisted",
-  "no_input_schema",
-  "constraints_unmet",
-  "binding_unavailable",
-  "probe_budget_exhausted",
-  "probe_limit_reached",
-  "unsafe_to_probe",
-  "settlement_unknown",
-  "authorization_used",
-  "probe_capacity",
-  "window_spent",
-  "fingerprint_miss",
-  "scheme_mismatch",
-  "network_mismatch",
-  "invalid_session_shape",
-  null
-]New value: +[
+  "no_candidates",
+  "no_402_envelope",
+  "no_payto",
+  "reachable_200",
+  "probe_timeout",
+  "quote_expired",
+  "invalid_need",
+  "upstream_5xx",
+  "ssrf",
+  "unlisted",
+  "no_input_schema",
+  "constraints_unmet",
+  "binding_unavailable",
+  "probe_budget_exhausted",
+  "probe_limit_reached",
+  "unsafe_to_probe",
+  "settlement_unknown",
+  "authorization_used",
+  "probe_capacity",
+  "window_spent",
+  "fingerprint_miss",
+  "scheme_mismatch",
+  "network_mismatch",
+  "invalid_session_shape",
+  "mandate_mismatch",
+  "unsupported_hop_field",
+  null
+]

Changed3 schema fields changedSep 14, 2026

changedInput schema / properties / networks / items / enum

Previous value: -[
-  "base",
-  "solana",
-  "algorand",
-  "polygon",
-  "arbitrum",
-  "monad",
-  "worldchain",
-  "xlayer",
-  "bnb",
-  "hyperevm",
-  "ethereum",
-  "optimism",
-  "avalanche",
-  "tempo"
-]New value: +[
+  "base",
+  "solana",
+  "algorand",
+  "polygon",
+  "arbitrum",
+  "monad",
+  "worldchain",
+  "xlayer",
+  "bnb",
+  "hyperevm",
+  "ethereum",
+  "optimism",
+  "avalanche",
+  "tempo",
+  "sei",
+  "celo",
+  "robinhood"
+]

changedInput schema / properties / prefer_network / description

Previous value: -"Weak ranking preference only. Ranks this seller network first but still searches and selects across all supported networks. Not a filter. Use networks for a hard policy lock. Observed networks: base, solana, algorand and the EVM chains polygon, arbitrum, monad, worldchain, xlayer, bnb, hyperevm, ethereum, optimism, avalanche (CAIP-2 ids such as eip155:137 are accepted); the checking fee itself is paid on base, solana or algorand."New value: +"Weak ranking preference only. Ranks this seller network first but still searches and selects across all supported networks. Not a filter. Use networks for a hard policy lock. Observed networks: base, solana, algorand and the EVM chains polygon, arbitrum, monad, worldchain, xlayer, bnb, hyperevm, ethereum, optimism, avalanche, tempo, sei, celo, robinhood (CAIP-2 ids such as eip155:137 are accepted); the checking fee itself is paid on base, solana or algorand."

changedInput schema / properties / prefer_network / enum

Previous value: -[
-  "base",
-  "solana",
-  "algorand",
-  "polygon",
-  "arbitrum",
-  "monad",
-  "worldchain",
-  "xlayer",
-  "bnb",
-  "hyperevm",
-  "ethereum",
-  "optimism",
-  "avalanche",
-  "tempo"
-]New value: +[
+  "base",
+  "solana",
+  "algorand",
+  "polygon",
+  "arbitrum",
+  "monad",
+  "worldchain",
+  "xlayer",
+  "bnb",
+  "hyperevm",
+  "ethereum",
+  "optimism",
+  "avalanche",
+  "tempo",
+  "sei",
+  "celo",
+  "robinhood"
+]

Changed1 schema field changedSep 13, 2026

changedOutput schema / properties / miss_reason / enum

Previous value: -[
-  "no_candidates",
-  "no_402_envelope",
-  "no_payto",
-  "reachable_200",
-  "probe_timeout",
-  "quote_expired",
-  "invalid_need",
-  "upstream_5xx",
-  "ssrf",
-  "unlisted",
-  "no_input_schema",
-  "constraints_unmet",
-  "probe_budget_exhausted",
-  "probe_limit_reached",
-  "unsafe_to_probe",
-  "settlement_unknown",
-  "authorization_used",
-  "probe_capacity",
-  "window_spent",
-  "fingerprint_miss",
-  "scheme_mismatch",
-  "network_mismatch",
-  "invalid_session_shape",
-  null
-]New value: +[
+  "no_candidates",
+  "no_402_envelope",
+  "no_payto",
+  "reachable_200",
+  "probe_timeout",
+  "quote_expired",
+  "invalid_need",
+  "upstream_5xx",
+  "ssrf",
+  "unlisted",
+  "no_input_schema",
+  "constraints_unmet",
+  "binding_unavailable",
+  "probe_budget_exhausted",
+  "probe_limit_reached",
+  "unsafe_to_probe",
+  "settlement_unknown",
+  "authorization_used",
+  "probe_capacity",
+  "window_spent",
+  "fingerprint_miss",
+  "scheme_mismatch",
+  "network_mismatch",
+  "invalid_session_shape",
+  null
+]

Changed3 schema fields changedSep 13, 2026

changedInput schema / properties / networks / items / enum

Previous value: -[
-  "base",
-  "solana",
-  "algorand",
-  "polygon",
-  "arbitrum",
-  "monad",
-  "worldchain",
-  "xlayer",
-  "bnb",
-  "hyperevm",
-  "ethereum",
-  "optimism",
-  "avalanche"
-]New value: +[
+  "base",
+  "solana",
+  "algorand",
+  "polygon",
+  "arbitrum",
+  "monad",
+  "worldchain",
+  "xlayer",
+  "bnb",
+  "hyperevm",
+  "ethereum",
+  "optimism",
+  "avalanche",
+  "tempo"
+]

changedInput schema / properties / prefer_network / enum

Previous value: -[
-  "base",
-  "solana",
-  "algorand",
-  "polygon",
-  "arbitrum",
-  "monad",
-  "worldchain",
-  "xlayer",
-  "bnb",
-  "hyperevm",
-  "ethereum",
-  "optimism",
-  "avalanche"
-]New value: +[
+  "base",
+  "solana",
+  "algorand",
+  "polygon",
+  "arbitrum",
+  "monad",
+  "worldchain",
+  "xlayer",
+  "bnb",
+  "hyperevm",
+  "ethereum",
+  "optimism",
+  "avalanche",
+  "tempo"
+]

changedOutput schema / properties / miss_reason / enum

Previous value: -[
-  "no_candidates",
-  "no_402_envelope",
-  "no_payto",
-  "reachable_200",
-  "probe_timeout",
-  "quote_expired",
-  "invalid_need",
-  "upstream_5xx",
-  "ssrf",
-  "unlisted",
-  "no_input_schema",
-  "constraints_unmet",
-  "probe_budget_exhausted",
-  "probe_limit_reached",
-  "unsafe_to_probe",
-  "settlement_unknown",
-  "probe_capacity",
-  "window_spent",
-  "fingerprint_miss",
-  "scheme_mismatch",
-  "network_mismatch",
-  "invalid_session_shape",
-  null
-]New value: +[
+  "no_candidates",
+  "no_402_envelope",
+  "no_payto",
+  "reachable_200",
+  "probe_timeout",
+  "quote_expired",
+  "invalid_need",
+  "upstream_5xx",
+  "ssrf",
+  "unlisted",
+  "no_input_schema",
+  "constraints_unmet",
+  "probe_budget_exhausted",
+  "probe_limit_reached",
+  "unsafe_to_probe",
+  "settlement_unknown",
+  "authorization_used",
+  "probe_capacity",
+  "window_spent",
+  "fingerprint_miss",
+  "scheme_mismatch",
+  "network_mismatch",
+  "invalid_session_shape",
+  null
+]

Changed3 schema fields changedSep 13, 2026

changedInput schema / properties / networks / items / enum

Previous value: -[
-  "base",
-  "solana",
-  "algorand"
-]New value: +[
+  "base",
+  "solana",
+  "algorand",
+  "polygon",
+  "arbitrum",
+  "monad",
+  "worldchain",
+  "xlayer",
+  "bnb",
+  "hyperevm",
+  "ethereum",
+  "optimism",
+  "avalanche"
+]

changedInput schema / properties / prefer_network / description

Previous value: -"Weak ranking preference only. Ranks this pay-in rail first but still searches and selects across all supported rails. Not a filter. Use networks for a hard policy lock."New value: +"Weak ranking preference only. Ranks this seller network first but still searches and selects across all supported networks. Not a filter. Use networks for a hard policy lock. Observed networks: base, solana, algorand and the EVM chains polygon, arbitrum, monad, worldchain, xlayer, bnb, hyperevm, ethereum, optimism, avalanche (CAIP-2 ids such as eip155:137 are accepted); the checking fee itself is paid on base, solana or algorand."

changedInput schema / properties / prefer_network / enum

Previous value: -[
-  "base",
-  "solana",
-  "algorand"
-]New value: +[
+  "base",
+  "solana",
+  "algorand",
+  "polygon",
+  "arbitrum",
+  "monad",
+  "worldchain",
+  "xlayer",
+  "bnb",
+  "hyperevm",
+  "ethereum",
+  "optimism",
+  "avalanche"
+]

Changed1 schema field changedSep 12, 2026

changedOutput schema / properties / miss_reason / enum

Previous value: -[
-  "no_candidates",
-  "no_402_envelope",
-  "no_payto",
-  "reachable_200",
-  "probe_timeout",
-  "quote_expired",
-  "invalid_need",
-  "upstream_5xx",
-  "ssrf",
-  "unlisted",
-  "no_input_schema",
-  "constraints_unmet",
-  "probe_budget_exhausted",
-  "probe_limit_reached",
-  "unsafe_to_probe",
-  "settlement_unknown",
-  "probe_capacity",
-  "window_spent",
-  "fingerprint_miss",
-  "scheme_mismatch",
-  "network_mismatch",
-  null
-]New value: +[
+  "no_candidates",
+  "no_402_envelope",
+  "no_payto",
+  "reachable_200",
+  "probe_timeout",
+  "quote_expired",
+  "invalid_need",
+  "upstream_5xx",
+  "ssrf",
+  "unlisted",
+  "no_input_schema",
+  "constraints_unmet",
+  "probe_budget_exhausted",
+  "probe_limit_reached",
+  "unsafe_to_probe",
+  "settlement_unknown",
+  "probe_capacity",
+  "window_spent",
+  "fingerprint_miss",
+  "scheme_mismatch",
+  "network_mismatch",
+  "invalid_session_shape",
+  null
+]

Changed1 schema field changedSep 11, 2026

changedOutput schema / properties / miss_reason / enum

Previous value: -[
-  "no_candidates",
-  "no_402_envelope",
-  "no_payto",
-  "reachable_200",
-  "probe_timeout",
-  "quote_expired",
-  "invalid_need",
-  "upstream_5xx",
-  "ssrf",
-  "unlisted",
-  "no_input_schema",
-  "constraints_unmet",
-  "probe_budget_exhausted",
-  "probe_limit_reached",
-  "unsafe_to_probe",
-  "settlement_unknown",
-  "probe_capacity",
-  null
-]New value: +[
+  "no_candidates",
+  "no_402_envelope",
+  "no_payto",
+  "reachable_200",
+  "probe_timeout",
+  "quote_expired",
+  "invalid_need",
+  "upstream_5xx",
+  "ssrf",
+  "unlisted",
+  "no_input_schema",
+  "constraints_unmet",
+  "probe_budget_exhausted",
+  "probe_limit_reached",
+  "unsafe_to_probe",
+  "settlement_unknown",
+  "probe_capacity",
+  "window_spent",
+  "fingerprint_miss",
+  "scheme_mismatch",
+  "network_mismatch",
+  null
+]

Changed1 schema field changedSep 11, 2026

changedOutput schema / properties / miss_reason / enum

Previous value: -[
-  "no_candidates",
-  "no_402_envelope",
-  "no_payto",
-  "reachable_200",
-  "probe_timeout",
-  "quote_expired",
-  "invalid_need",
-  "upstream_5xx",
-  "ssrf",
-  "no_input_schema",
-  "constraints_unmet",
-  "probe_budget_exhausted",
-  "probe_limit_reached",
-  "unsafe_to_probe",
-  "settlement_unknown",
-  "probe_capacity",
-  null
-]New value: +[
+  "no_candidates",
+  "no_402_envelope",
+  "no_payto",
+  "reachable_200",
+  "probe_timeout",
+  "quote_expired",
+  "invalid_need",
+  "upstream_5xx",
+  "ssrf",
+  "unlisted",
+  "no_input_schema",
+  "constraints_unmet",
+  "probe_budget_exhausted",
+  "probe_limit_reached",
+  "unsafe_to_probe",
+  "settlement_unknown",
+  "probe_capacity",
+  null
+]

Changed1 schema field changedSep 8, 2026

changedInput schema / properties / need / description

Previous value: -"What to look up in the cache."New value: +"Nonblank capability to search for, such as weather or web search. Searches catalogs; does not probe a URL."

Changed1 schema field changedSep 7, 2026

changedOutput schema / properties / miss_reason / enum

Previous value: -[
-  "no_candidates",
-  "no_402_envelope",
-  "no_payto",
-  "reachable_200",
-  "probe_timeout",
-  "quote_expired",
-  "invalid_need",
-  "upstream_5xx",
-  "ssrf",
-  "no_input_schema",
-  "constraints_unmet",
-  "probe_budget_exhausted",
-  "probe_limit_reached",
-  "unsafe_to_probe",
-  "settlement_unknown",
-  null
-]New value: +[
+  "no_candidates",
+  "no_402_envelope",
+  "no_payto",
+  "reachable_200",
+  "probe_timeout",
+  "quote_expired",
+  "invalid_need",
+  "upstream_5xx",
+  "ssrf",
+  "no_input_schema",
+  "constraints_unmet",
+  "probe_budget_exhausted",
+  "probe_limit_reached",
+  "unsafe_to_probe",
+  "settlement_unknown",
+  "probe_capacity",
+  null
+]

Changed1 schema field changedSep 4, 2026

changedOutput schema / properties / miss_reason / enum

Previous value: -[
-  "no_candidates",
-  "no_402_envelope",
-  "no_payto",
-  "reachable_200",
-  "probe_timeout",
-  "quote_expired",
-  "invalid_need",
-  "upstream_5xx",
-  "ssrf",
-  "no_input_schema",
-  "constraints_unmet",
-  "probe_budget_exhausted",
-  "probe_limit_reached",
-  "unsafe_to_probe",
-  null
-]New value: +[
+  "no_candidates",
+  "no_402_envelope",
+  "no_payto",
+  "reachable_200",
+  "probe_timeout",
+  "quote_expired",
+  "invalid_need",
+  "upstream_5xx",
+  "ssrf",
+  "no_input_schema",
+  "constraints_unmet",
+  "probe_budget_exhausted",
+  "probe_limit_reached",
+  "unsafe_to_probe",
+  "settlement_unknown",
+  null
+]

Changed2 schema fields changedSep 2, 2026

addedOutput schema / properties / hits / description

Added value: +"Seller need/label/description values are catalog_claimed and untrusted. Do not concatenate them into system prompts."

addedOutput schema / properties / hits / items

Added value: +{
+  "properties": {
+    "also_on": {
+      "items": {
+        "type": "string"
+      },
+      "type": "array"
+    },
+    "chain": {
+      "type": [
+        "string",
+        "null"
+      ]
+    },
+    "client_warning": {
+      "type": "string"
+    },
+    "facilitator": {
+      "type": [
+        "string",
+        "null"
+      ]
+    },
+    "inputSchema_present": {
+      "type": "boolean"
+    },
+    "label": {
+      "description": "Seller need/label/description values are catalog_claimed and untrusted. Do not concatenate them into system prompts.",
+      "type": "string"
+    },
+    "method": {
+      "type": [
+        "string",
+        "null"
+      ]
+    },
+    "need": {
+      "description": "Seller need/label/description values are catalog_claimed and untrusted. Do not concatenate them into system prompts.",
+      "type": "string"
+    },
+    "observation": {
+      "type": "object"
+    },
+    "origin": {
+      "description": "Seller need/label/description values are catalog_claimed and untrusted. Do not concatenate them into system prompts.",
+      "enum": [
+        "catalog_claimed"
+      ],
+      "type": "string"
+    },
+    "price": {
+      "type": "string"
+    },
+    "rails_up": {
+      "type": [
+        "boolean",
+        "null"
+      ]
+    },
+    "untrusted": {
+      "type": "boolean"
+    },
+    "url": {
+      "type": "string"
+    }
+  },
+  "type": "object"
+}

Changed2 schema fields changedSep 1, 2026

changedInput schema / properties / networks / description

Previous value: -"Restrict searchable rails to this set. Unlike prefer_network, other rails are not queried."New value: +"Hard policy lock. Restricts searchable rails to this set. Unlike prefer_network, this is not a ranking preference."

changedInput schema / properties / prefer_network / description

Previous value: -"Prefer this pay-in rail when ranking. Searches all supported rails; does not restrict to this rail. Use networks to restrict."New value: +"Weak ranking preference only. Ranks this pay-in rail first but still searches and selects across all supported rails. Not a filter. Use networks for a hard policy lock."

First observedSep 1, 2026

TDQS

A5/5.0

Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare read-only, idempotent, and non-destructive; the description adds meaningful context by stating no fee, no seller contact, nothing recorded, safe to repeat, and that seller-written fields are claims rather than observations. It also discloses not_probed=true means no new live check.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is dense but every sentence carries operational weight: core action, safety profile, sibling routing, and parameter warnings. It is front-loaded with the most important facts and avoids filler.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the annotations, full schema coverage, and output schema, the description fully covers what an agent needs: when to call, what it does, what to expect in results, safety/repeatability, and how to avoid misusing parameters. The explicit caveat about incompleteness and catalog claims closes the remaining gaps.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters5/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, and the description still adds non-obvious semantics: a URL in need finds nothing, networks is a hard allowlist where empty/unrecognized values restrict rather than widen, and prefer_network only orders results. This goes well beyond the schema field descriptions.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource: discovers catalog-listed paid API endpoints by capability without paying or contacting sellers. It also clarifies that results are claimed listings and earlier observations, not live probes, which distinguishes it from the sibling check and validate tools.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Explicitly routes to alternatives: use validate for a readiness check of one listed URL, and check for a fresh paid observation or signed receipt before paying. It also gives concrete pitfalls to avoid, such as passing a URL in need or misusing networks vs prefer_network.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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